RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v16]

[Johannes Bechberger]

On Mon, 26 May 2025 19:58:26 GMT, Robert Toyonaga <duke at openjdk.org> wrote:

>> Johannes Bechberger has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove mistake
>
> src/hotspot/share/jfr/recorder/service/jfrEventThrottler.cpp line 89:
> 
>> 87:   }
>> 88:   if (event_id == JfrCPUTimeSampleEvent) {
>> 89:     return _disabled_cpu_time_sample_throttler;
> 
> Why do you need to make a "disabled" throttler? Shouldn't the rate limiting always be done by the arguments given to `timer_create`? The actual JFR throttling mechanism used by `ObjectAllocationSample` doesn't really fit this use-case anyway since you can already pre-determine the rate at which events are emitted (while with `ObjectAllocationSample` you can't).

This just makes the code simpler and avoids two additional checks on the throttler hot-path. The _disabled_cpu_time_sample_throttler is like `nullptr` but without the `nullptr` check.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2107813533